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minio/cmd/http/dial_dnscache.go

197 lines
4.9 KiB

/*
* MinIO Cloud Storage, (C) 2020 MinIO, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package http
import (
"context"
"log"
"math/rand"
"net"
"sync"
"time"
)
var randPerm = func(n int) []int {
return rand.Perm(n)
}
// DialContextWithDNSCache is a helper function which returns `net.DialContext` function.
// It randomly fetches an IP from the DNS cache and dials it by the given dial
// function. It dials one by one and returns first connected `net.Conn`.
// If it fails to dial all IPs from cache it returns first error. If no baseDialFunc
// is given, it sets default dial function.
//
// You can use returned dial function for `http.Transport.DialContext`.
//
// In this function, it uses functions from `rand` package. To make it really random,
// you MUST call `rand.Seed` and change the value from the default in your application
func DialContextWithDNSCache(cache *DNSCache, baseDialCtx DialContext) DialContext {
if baseDialCtx == nil {
// This is same as which `http.DefaultTransport` uses.
baseDialCtx = (&net.Dialer{
Timeout: 30 * time.Second,
KeepAlive: 30 * time.Second,
DualStack: true,
}).DialContext
}
return func(ctx context.Context, network, host string) (net.Conn, error) {
h, p, err := net.SplitHostPort(host)
if err != nil {
return nil, err
}
// Fetch DNS result from cache.
//
// ctxLookup is only used for canceling DNS Lookup.
ctxLookup, cancelF := context.WithTimeout(ctx, cache.lookupTimeout)
defer cancelF()
addrs, err := cache.Fetch(ctxLookup, h)
if err != nil {
return nil, err
}
var firstErr error
for _, randomIndex := range randPerm(len(addrs)) {
conn, err := baseDialCtx(ctx, "tcp", net.JoinHostPort(addrs[randomIndex], p))
if err == nil {
return conn, nil
}
if firstErr == nil {
firstErr = err
}
}
return nil, firstErr
}
}
const (
// cacheSize is initial size of addr and IP list cache map.
cacheSize = 64
)
// defaultFreq is default frequency a resolver refreshes DNS cache.
var (
defaultFreq = 3 * time.Second
defaultLookupTimeout = 10 * time.Second
)
// DNSCache is DNS cache resolver which cache DNS resolve results in memory.
type DNSCache struct {
sync.RWMutex
lookupHostFn func(ctx context.Context, host string) ([]string, error)
lookupTimeout time.Duration
cache map[string][]string
closer func()
}
// NewDNSCache initializes DNS cache resolver and starts auto refreshing
// in a new goroutine. To stop auto refreshing, call `Stop()` function.
// Once `Stop()` is called auto refreshing cannot be resumed.
func NewDNSCache(freq time.Duration, lookupTimeout time.Duration) *DNSCache {
if freq <= 0 {
freq = defaultFreq
}
if lookupTimeout <= 0 {
lookupTimeout = defaultLookupTimeout
}
ticker := time.NewTicker(freq)
ch := make(chan struct{})
closer := func() {
ticker.Stop()
close(ch)
}
r := &DNSCache{
lookupHostFn: net.DefaultResolver.LookupHost,
lookupTimeout: lookupTimeout,
cache: make(map[string][]string, cacheSize),
closer: closer,
}
go func() {
for {
select {
case <-ticker.C:
r.Refresh()
case <-ch:
return
}
}
}()
return r
}
// LookupHost lookups address list from DNS server, persist the results
// in-memory cache. `Fetch` is used to obtain the values for a given host.
func (r *DNSCache) LookupHost(ctx context.Context, host string) ([]string, error) {
addrs, err := r.lookupHostFn(ctx, host)
if err != nil {
return nil, err
}
r.Lock()
r.cache[host] = addrs
r.Unlock()
return addrs, nil
}
// Fetch fetches IP list from the cache. If IP list of the given addr is not in the cache,
// then it lookups from DNS server by `Lookup` function.
func (r *DNSCache) Fetch(ctx context.Context, host string) ([]string, error) {
r.RLock()
addrs, ok := r.cache[host]
r.RUnlock()
if ok {
return addrs, nil
}
return r.LookupHost(ctx, host)
}
// Refresh refreshes IP list cache, automatically.
func (r *DNSCache) Refresh() {
r.RLock()
hosts := make([]string, 0, len(r.cache))
for host := range r.cache {
hosts = append(hosts, host)
}
r.RUnlock()
for _, host := range hosts {
ctx, cancelF := context.WithTimeout(context.Background(), r.lookupTimeout)
if _, err := r.LookupHost(ctx, host); err != nil {
log.Println("failed to refresh DNS cache, resolver is unavailable", err)
}
cancelF()
}
}
// Stop stops auto refreshing.
func (r *DNSCache) Stop() {
r.Lock()
defer r.Unlock()
if r.closer != nil {
r.closer()
r.closer = nil
}
}